How can you avoid being taken by one of these crooks when selling band candy, or holding a yard sale, or taking part in other casual commerce?

I asked this question of Jamie Fitch, agent-in-charge of the Columbus, Ohio, Secret Service resident office.

He said, "First, never put yourself in jeopardy." This makes perfect sense to me. Is losing the change from a $20 or even $100 bill worth the risk of confronting a criminal? Before you give in to your anger, consider the danger.

He then suggests learning how to identify a fake bill. If someone offers one to you, you could claim a lack of change, or feign sympathy with the person trying to pass it by saying something like, "Maybe you got ripped off, too."

I'd add that keeping your money out of sight at all times makes claiming a lack of change easier. Another option is to discretely call the police, if possible.

If you do find bad money in your kitty at the end of the day, you can either take it to your bank, which is obligated to pass it along to the Secret Service, or send it directly to the Service. If you can provide a good description of the perp, it will help the subsequent investigation.

I intended to recommend buying one of the cheap counterfeit detection pens like you see cashiers use, but Fitch told me the Service doesn't recommend them. He explained that the pens use an iodine solution which reacts with starch. Since U.S. bills contain no starch, while photocopied bills do, this should differentiate the two. However, our currency can easily pick up some starch while in circulation, leading to false positives.

Fitch recommends detecting fakes by using your eyes and fingers. The feel of real money, he told me, is noticeably different than that of copies. The Secret Service recommends examining:

The portrait; if it is lifeless and flat, or the details are mottled, it may be a fake.

The edges of the Federal Reserve and Treasury seals, which should be sharp and distinct.

The delicate, ornate lines on the outside border of the bill, which should be unbroken and crisp.

The serial numbers, which should be evenly spaced. The ink should match the seal.

The paper. It should have minute threads of red and blue embedded throughout. Your hand can sometimes tell you what your eyes cannot.

The denomination. Scammers often clip the corner numbers from a high-value bill and past them onto lower value ones. Remember, George Washington is not on the $10 or $100 bill. And check every $20 to make sure it isn't a $2; they're so uncommon the mistake is easy to make.

Look for color-shifting ink on new series bills (the multi-colored ones) except the $5: the numeral in the lower right corner should shift from green to black as you rotate the bill.

Hold the bill up to the light and check that the watermark is visible to the right of the portrait.

Also check that the bill has a security thread embedded, running from top to bottom.

On the security thread should be micro-printed "USA 50," the number changing to match the denomination.

If you do end up with counterfeit money, I'm sorry to tell you you'll have to eat the loss; there is no reward program. The frugal WalletPopper, then, will keep the bad stuff from making its way into our purses and wallets in the first place.